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Discussion Starter · #1 ·
Hi, need Help in picking replacement Central HVAC system for our house the Square footage of the home is 1,990, and the zip code is 94520 for our climate we get 80, 90, and low 100 degrees in the summer, in the winter we get upper 30 to 40 degrees at night our home doesn't have good insulation in attic but did have newer dual pane windows with low e glass, our current HVAC system is Rheem from 1972 or 1973 the Natural Gas Furnace Model number 3010 125 HDA input is 125,000 BTU, and the Bonnet is 100,000BTU the outside condenser Model number is AT42B1 not sure if that is 4 Ton unit, also seeing that the new HVAC system are so much more Efficient would we need smaller system? I was looking at Different ones we will have HVAC contractor install it but wanted to do some research I found this one Rheem 95% 98,000 BTU 2 Stage Furnace + 4 Ton 15.1 SEER A/C on Ebay item number 182163860369

any help would be appreciated
 

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Are the walls 2x4 and insulated?

Square footage doesn't mean that much on it's own, construction type and exterior surface area mean a lot.

I can tell you that the furnace is grossly oversized.

Where I am where it hits -5f a few nights per year, a well insulated 2000 sq ft detached house can heat easily with a 60 000 btu input/57k output furnace, with capacity to spare.

A load calculation would need to be done. You may only need a 40000 or 60000 btu input to heat that house in your climate.




Now, if you go for 4 tons of cooling, you'll need at least an 80 000 btu input furnace to deliver the 1600 cfm 4 tons need, and a lot of models at that capacity will come with 1200 cfm blower.

More efficient equipment is sized the same way, just that for furnaces you have to check the output and not the input.

With a load calculation, you may find that you only need a 3 or 3.5 ton a/c.


Note: Ductwork in attic will reduce delivered capacity. load calc software allows u to factor that in.

About purchasing equipment online;

you'll be much better off finding a contractor to do it. This stuff has to be done right or not at all.

Gas lines and venting if not done correctly can kill you.

for a/c u would need a license, recovery machine, gauges, vacuum pump, brazing torches and more.

If you insist on purchasing stuff online, avoid ebay. Purchase from a company with a good return policy and support; i know of alpine indoor air. they sell goodman stuff.
 

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You need to do a manual j, manual d, and manual s to properly size the system. Square footage and the size of the previous system doesn't tell you too much.
eBay is not an hvac supply source. You'll get no warranty.
I'd suggest either doing it yourself or letting a contractor do the job. A lot can go wrong if you try and supply equipment and find someone to slap it in.
 

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Some reading material and things that need to be considered. Remember this isn't like buying a normal appliance or even a car. This is something that comes in pieces and must be put together and commissioned correctly to get it to function right.

https://www.angieslist.com/articles/difference-between-best-hvac-brands.htm

http://efficientcomfort.net/documents/Understanding_HVAC_System_Design_Issues.pdf

http://efficientcomfort.net/documents/Sizing_&_Selecting_for_Proper_Humidity_Control.pdf

http://efficientcomfort.net/documents/Bigger_is_Not_Better-Sizing_Air_Conditioners_Properly.pdf

www.loadcalc.net
 

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Your current A/C may only be a 3.5 ton by that model number.

A 3 ton low efficiency(8 SEER) A/C is a nominal 36,000 BTUs. A 2 ton 21 SEER A/C is only a nominal 24,000 BTUs. So no, a higher efficiency A/C doesn't mean that you can use a smaller A/C.

A load alc can determine if your current A/C is larger then needed.
 

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Discussion Starter · #6 ·
Hi, Thanks for all the help everyone

Are the walls 2x4 and insulated? No the outside walls of the home is not insulated

the Ductwork runs in the crawlspace

HVAC intake duct is in the attic
 

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Might want to get the walls insulated before you go any further.
 

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Often from the inside. drill a 2 to 2.5" hole in wall, blow in insulation, then repair hole.
 
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